The present invention relates to curing systems based on polysulfide derivatives of 1,3,4-thiadiazole and their use in curing chlorine-containing polymers.
In the past, chlorine-containing polymers have been compounded with curatives and other ingredients for vulcanization into vulcanizates for use in various industrial and consumer applications. Many known curing accelerators, however, are highly active at relatively low temperatures and consequently may cause premature vulcanization or scorching. This phenomenon my lead to unsatisfactory physical properties of the vulcanizate.
One type of accelerators based on 2,5-dimercapto-1,3,4-thiadiazole is disclosed in U.S. Pat. No. 4,128,510.
A disadvantage of known 1,3,4-thiadiazole curing agents is poor bin storage stability. That is, the viscosity tends to increase during storage of the chlorinated polymer compounded with the thiadiazole based curative. The increased viscosity requires tedious process control, as for example frequent adjustment of machine settings.
Surprisingly, it has been discovered that certain organopolysulfide derivatives of 1,3,4-thiadiazole are effective curing agents for chlorinated polymers and furthermore, display excellent bin storage stability when compounded with the polymer.